Sodium channels play a crucial role in the nervous and the muscle excitability. They are targeted by a variety of natural and synthetic toxins. Some of them show high selectivity to insects. They are considered as potential bioinsecticides. Toxins bind to different sites in sodium channel; moreover allosteric interactions have been observed between them. Interactions between scorpion insect selective sodium channel toxins (alpha and excitatory toxins) binding to sites 3 and 4, and classical insecticides - pyrethroids (deltamethrin and permethrin – binding to site 7) have been tested at the cellular and whole insect organism level. In cockroach (Periplaneta am.) isolated giant axon preparation, the application of scorpion toxins, in “threshold” concentration, accelerated the development of pyrethroid effects. Afterwards, action of pyrethroids in control conditions and after pretreatement with scorpion toxins was tested on DUM (dorsal unpaired median) cockroach neurons. Recordings were realized in “in situ” conditions. Surprisingly, the presence of toxins did not increase the pyrethroid effects – rather slowed them down. Tests performed on whole insects confirmed this strange effect. Scorpion toxins have been applied in the vicinity of cockroach nerve cord, at dose inducing soft insect excitation. Effect of post-application of pyrethroids has been observed. Pretreatment with scorpion toxins did not increase much or not at all the effects of pyrethroids. Studies are continued with different doses of toxins as well as of pyrethroids on neuronal and whole insect level. The aim is to clarify why the synergistic activity and even the summation of the two component effects was not observed. Results may be crucial for pest insect control, whereas co-application of different agents is proposed as a presenttime practice. Work was sponsored by the Ministry of Science and Higher Education, project no. N N303 320637
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